JP2005-30534A, published by the Japan Patent Office in 2005, proposes an inverted tube-type front fork adapted to be interposed between a vehicle body and a front wheel axis of a motorcycle. The front fork comprises a damper for absorbing oscillation input into the front wheel from running surface.
In this front fork, an inner tube connected to the wheel axis is inserted into an outer tube connected to the vehicle body so as to be free to slide. The damper is disposed in the interior of these tubes. The damper comprises a damper cylinder projecting downward from an upper end of the outer tube, a piston rod projecting upward from a bottom of the inner tube and having a tip inserted into the damper cylinder, and a piston fixed to a tip end of the piston rod in the damper cylinder.
The piston is in contact with an inner circumference of the damper cylinder so as to be free to slide in the axial direction and delimits an upper oil chamber above the piston and a lower oil chamber below the piston in the damper cylinder. As the piston slides axially in the damper cylinder, the capacity of these two oil chambers varies. The piston comprises a damping valve and a check valve which cause working oil in the oil chambers to flow therethrough depending on variation in the capacity of the two oil chambers.
The total capacity of the two oil chambers varies depending on a penetration volume of the piston rod into the damper cylinder. In order to compensate for oil amount variation in the damper cylinder due to this capacity variation, an oil reservoir is provided above the upper oil chamber in the damper cylinder. The oil reservoir is separated from the upper oil chamber by a base valve and an upper end of the oil reservoir is delimited by a free piston which is fitted into the inner circumference of the camper cylinder so as to be free to slide. The free piston is biased in a direction to compress the oil reservoir using compressed air in an air chamber formed above the free piston and a spring enclosed in the air chamber.
Further, a space having a ring-shaped cross section between the damper cylinder and the outer/inner tubes is utilized as an auxiliary reservoir in which air and working oil are enclosed.